Temperature-insensitive calcium phosphate cements

ABSTRACT

Temperature-insensitive calcium phosphate cements and methods of using the same are provided. Aspects of the cements include a dry component having fine and coarse calcium phosphate particulate reactants and a setting fluid which includes a cellulose. The dry component and setting fluid may be combined over a broad temperature range to produce a flowable composition. The resultant flowable composition finds use in a variety of different applications, including the repair of hard tissue defects, e.g., bone defects such as fractures.

INTRODUCTION

Calcium phosphate cements find use as structural materials in theorthopedic and dental fields. Such cements are typically prepared bycombining a dry component(s) and a liquid to form a flowable paste-likematerial that is subsequently capable of setting into a solid calciumphosphate product. Materials that set into solid calcium phosphatemineral products are of particular interest as such products can closelyresemble the mineral phase of natural bone and are susceptible toremodeling, making such products extremely attractive for use inorthopedics and related fields.

While a large number of different calcium phosphate cement formulationshave been developed, there is a continued need for the development ofyet more advanced formulations. For example, calcium phosphate cementsare highly temperature sensitive requiring use at specific temperaturesranging between 19° C. to 22° C. Below 19° C., calcium phosphate cementstend to be very runny and show signs of decreased mechanical properties.Above 22° C., many calcium phosphate cements tend to be dry and crumbleafter mixing, presenting problems during use, e.g., injection into abone repair site. Such problems limit the use of calcium phosphatecements in the surgical field.

SUMMARY

Temperature-insensitive calcium phosphate cements and methods of usingthe same are provided. Aspects of the cements include a dry componenthaving fine and coarse calcium phosphate particulate reactants and asetting fluid which includes a cellulose. The dry component and settingfluid may be combined over a broad temperature range to produce aflowable composition. The resultant flowable composition finds use in avariety of different applications, including the repair of hard tissuedefects, e.g., bone defects such as fractures.

DETAILED DESCRIPTION

Temperature-insensitive calcium phosphate cements and methods of usingthe same are provided. Aspects of the cements include a dry componenthaving fine and coarse calcium phosphate particulate reactants and asetting fluid which includes a cellulose. The dry component and settingfluid may be combined over a broad temperature range to produce aflowable composition. The resultant flowable composition finds use in avariety of different applications, including the repair of hard tissuedefects, e.g., bone defects such as fractures.

Before the present invention is further described, it is to beunderstood that this invention is not limited to particular embodimentsdescribed, as such may, of course, vary. It is also to be understoodthat the terminology used herein is for the purpose of describingparticular embodiments only, and is not intended to be limiting, sincethe scope of the present invention will be limited only by the appendedclaims.

Where a range of values is provided, it is understood that eachintervening value, to the tenth of the unit of the lower limit unlessthe context clearly dictates otherwise, between the upper and lowerlimit of that range and any other stated or intervening value in thatstated range, is encompassed within the invention. The upper and lowerlimits of these smaller ranges may independently be included in thesmaller ranges and are also encompassed within the invention, subject toany specifically excluded limit in the stated range. Where the statedrange includes one or both of the limits, ranges excluding either orboth of those included limits are also included in the invention.

Methods recited herein may be carried out in any order of the recitedevents which is logically possible, as well as the recited order ofevents.

Unless defined otherwise, all technical and scientific terms used hereinhave the same meaning as commonly understood by one of ordinary skill inthe art to which this invention belongs. Although any methods andmaterials similar or equivalent to those described herein can also beused in the practice or testing of the present invention, the preferredmethods and materials are now described.

It must be noted that as used herein and in the appended claims, thesingular forms “a”, “an”, and “the” include plural referents unless thecontext clearly dictates otherwise. It is further noted that the claimsmay be drafted to exclude any optional element. As such, this statementis intended to serve as antecedent basis for use of such exclusiveterminology as “solely,” “only” and the like in connection with therecitation of claim elements, or use of a “negative” limitation.

All publications mentioned herein are incorporated herein by referenceto disclose and describe the methods and/or materials in connection withwhich the publications are cited.

The publications discussed herein are provided solely for theirdisclosure prior to the filing date of the present application. Nothingherein is to be construed as an admission that the present invention isnot entitled to antedate such publication by virtue of prior invention.Further, the dates of publication provided may be different from theactual publication dates which may need to be independently confirmed.

Calcium Phosphate Cements and Methods of Using the Same

As summarized above, aspects of the invention includetemperature-insensitive calcium phosphate cements. As the cements aretemperature-insensitive calcium phosphate cements, the dry componentsand setting fluid can be combined over a broad temperature range andproduce a consistent, flowable composition that sets into a desiredcalcium phosphate product. By consistent is meant that the flowablecomposition does not vary with respect to its properties (e.g., settingtime, flow properties, strength of set product, etc.) despite beingproduced at any particular temperature over a broad temperature range.In some instances, the dry components and setting fluid are combined ata temperature ranging anywhere from 15 to 25° C., where in someinstances the temperature is between 15 and 19° C., e.g., between 16 and18.5° C.; and in some instances the temperature is between 22 and 25°C., e.g., 22.5 and 25° C. Over this broad temperature range, aconsistent flowable composition is produced. As such, the dry componentsand setting fluid may be combined at any of the following temperatures,or a temperature in between any one of the following temperatures, andstill provide a consistent product: 15° C., 16° C., 17° C., 18° C., 19°C., 20° C., 21° C., 22° C., 23° C., 24° C. and 25° C., in certainembodiments.

Aspects of calcium phosphate cements of embodiments of the inventioninclude a dry reactant component that includes a first fine particulatecalcium phosphate reactant having a mean particle size of 8 μm or less;and a second coarse calcium phosphate reactant having a mean particlesize that is 10 μm or greater.

The fine particulate calcium phosphate reactant is a calcium and/orphosphate dry reactant, e.g., a calcium phosphate mineral, having a meanparticle size (as determined using the Horiba LA-300 laser diffractionparticle sizer (Version 3.30 software for Windows 95)(Irvine, Calif.))of 8 μm or less and a narrow particle size distribution. The meanparticle size of this fine particle reactant may vary, ranging incertain embodiments from 1 to 7 μm, such as from 1 to 6 μm, includingfrom 1 to 5 μm, where the mean particle size of the fine particlereactant in certain embodiments may be 1, 2, 3 and 4 μm, where incertain embodiments the mean particle size is 3 μm. The fine particlereactant is further characterized by having a narrow particle sizedistribution. By narrow particle size distribution is meant that thestandard deviation of the particles that make up the fine particlereactant (as determined using the Horiba LA-300 laser diffractionparticle sizer (Version 3.30 software for Windows 95)(Irvine, Calif.))is 4.0 μm or less, and in certain embodiments is 3.0 μm or less, e.g.,2.5 μm or less, including 2.0 μm or less. The fine particulate reactantis further characterized in that the mode (as determined using theHoriba LA-300 laser diffraction particle sizer (Version 3.30 softwarefor Windows 95)(Irvine, Calif.)) is 8.0 μm or less, and in certainembodiments 6.0 μm or less, e.g., 5 μm or less, including 3.0 μm orless. In certain embodiments, the fine particulate reactant is a calciumphosphate compound having a calcium to phosphate ratio ranging from 1.0to 2.0, including from 1.33 to 1.67, such as 1.5. Calcium phosphates ofinterest include include: MCPM (monocalcium phosphate monohydrate orCa(H₂PO₄)₂.H₂O); DCPD (dicalcium phosphate dihydrate, brushite orCaHPO₄.2H₂O), ACP (amorphous calcium phosphate or Ca₃(PO₄)₂H₂O), DCP(dicalcium phosphate, monetite or CaHPO₄), tricalcium phosphate,including both α- and β-(Ca₃(PO₄)₂, tetracalcium phosphate (Ca₄(PO₄)₂O,etc. In certain embodiments, the calcium phosphate compound is atricalcium phosphate, such as α- and β-tricalcium phosphate, where incertain embodiments, the tricalcium phosphate is α-tricalcium phosphate.

Also present in the dry reactant component is a second coarse calciumphosphate reactant having a mean particle size that is 10 μm or greater.In certain embodiments, the particle size of this second reactant is 20μm or greater, such as 25 μl or greater, including 30 μm or greater (asdetermined using the Horiba LA-300 laser diffraction particle sizer(Version 3.30 software for Windows 95)(Irvine, Calif.)), such as 50 μmor greater, 100 μm or greater, 150 μm or greater, including 200 μm orgreater, where the particle size of this second reactant may range from10 to 500 μm, such as from 25 to 250 μm. Calcium phosphates of interestinclude: MCPM (monocalcium phosphate monohydrate or Ca(H₂PO₄)₂.H₂O);DCPD (dicalcium phosphate dihydrate, brushite or CaHPO₄.2H₂O), ACP(amorphous calcium phosphate or Ca₃(PO₄)₂H₂O), DCP (dicalcium phosphate,monetite or CaHPO₄), tricalcium phosphate, including both α- andβ-(Ca₃(PO₄)₂, tetracalcium phosphate (Ca₄(PO₄)₂O, etc. In certainembodiments, the calcium phosphate compound is a tricalcium phosphate,such as α- and β-tricalcium phosphate.

In certain embodiments, the second coarse particle calcium phosphatereactant is α-tricalcium phosphate. In these embodiments, the dryreactants include a tricalcium phosphate coarse particle compositionthat has mean particle size that is at least 2 times larger than themean particle size of the fine particles component, where the meanparticle size of coarse particle component may be 20 μm or larger, 30 μmor larger, 40 μm or larger (as determined using the Horiba LA-300 laserdiffraction particle sizer (Version 3.30 software for Windows95)(Irvine, Calif.)), such as 50 μm or larger, 100 μm or larger, 150 μmor larger, 200 μm or larger, where the particle size of the tricalciumphosphate coarse particle component population (also referred to hereinas a coarse particle size population) may range from 10 to 500 μm, suchas from 25 to 250 μm. In certain instances, the particles of thiscomponent can range in size from 38 μm to 212 μm, such as from 38 μm to106 μm or 106 μm to 212 μm. In some instances, the coarse particlereactant is produced by the methods described in U.S. patent applicationSer. No. 12/328,720; the disclosure of which is herein incorporated byreference.

In certain embodiments, the amount of the fine particle reactant in thedry reactant component is greater than the total amount of otherreactants that may be present in the dry reactant component, such as thecoarse particle reactant as described herein. In these embodiments, themass ratio of the fine particle reactant to the total mass of the dryreactants of the dry reactant component may range from 1 to 10, e.g.,from 9 to 6, such as from 9 to 7, including from 9.5 to 8.5.

The ratios or relative amounts of each of the disparate fine and coarseparticle reactants in the dry reactant component is one that providesfor the desired calcium phosphate product upon combination of the dryreactant component with the setting fluid and subsequent setting. Incertain embodiments, the overall ratio of all of the disparate calciumand/or phosphate compounds in the dry reactants in terms of the calciumto phosphate ration in the dry reactant component ranges from 4:1 to0.5:1, usually from 2:1 to 1:1 and more usually from 1.9:1 to 1.33:1.

The fine and coarse particle reactants may be made up of the same ordifferent compounds, e.g., the same or different calcium minerals, suchas the same or different calcium phosphate minerals. For example, incertain embodiments of interest, the dry reactant component includesboth coarse and fine particles of the same calcium containing mineral,e.g., α-tricalcium phosphate. In yet other embodiments, a portion, ifnot all of the coarse population of particles is made up of one or moredifferent calcium containing compounds as compared to the compoundmaking up the fine particle size population. For example, in certainembodiments, one may have a fine particle reactant made up of a firstcalcium containing compound, e.g., α-tricalcium phosphate particles, anda coarse particle reactant made up of a second calcium containingcompound that differs in some way from the compound making up the firstpopulation, e.g., in terms of phase, molecular formula, solubility,radiopacity, etc. In certain embodiments, the fine and coarse particlereactants will be made up of different phases of the same calciumcontaining compound, such as the same calcium phosphate containingcompound. For example, the coarse and fine particle size reactants couldboth be made up of tricalcium phosphate, but the fine particle reactantcould be made up of α-tricalcium phosphate while the coarse particlereactant is made up of β-tricalcium phosphate particles, such that whilethe fine and coarse particle reactants are made up of the same compound,they are made up of different phases of the same compound, where thedifferent phases differ from each other at least in terms of solubility.In yet other embodiments, the different reactants may be made up ofdifferent compounds, e.g., that differ from each other in terms ofmolecular formula, radiopacity, solubility, combinations thereof, etc.For example, in certain embodiments the fine particle reactant is madeup of α-tricalcium phosphate particles, and a coarse particle reactantis made up at least partially of a different calcium containingcompound, e.g., that differs in terms of at least molecular formula, ifnot radiopacity. For example, the coarse particle reactant may include acalcium containing compound that is not a tricalcium phosphate, such asin those embodiments where the coarse particle reactant is made up of acombination of β-tricalcium phosphate particles and particles ofdolomite (CaMgCO₃).

In certain embodiments, the cements may further include an amount of anemulsifying agent, as described in U.S. application Ser. No. 11/134,051(published as US 2005-0260279); the disclosure of which is hereinincorporated by reference in its entirety. Emulsifying agents ofinterest include, but are not limited to: polyoxyethylene orpolyoxypropylene polymers or copolymers thereof, such as polyethyleneglycol and polypropylene glycol; nonionic cellulose ethers such asmethylcellulose, ethylcellulose, hydroxymethylcellulose,hydroxyethylcellulose, carboxymethylcellulose, carboxyethylcellulose andhydroxypropylcellulose; additional celluloses, such ascarboxymethylcellulose sodium, carboxymethylcellulose calcium,carboxymethylstarch; polysaccharides produced by microbial fermentation,such as yeast glucans, xanthan gum, β-1,3-glucans (which may bestraight-chained or branched; e.g. curdlan, paramylum, pachyman,scleroglucan, laminaran); other natural polymers, e.g., gum arabic, guargum, carrageenin, gum tragacanth, pectin, starch, gelatin, casein,dextrin, cellulose; polyacrylamide; polyvinyl alcohol; starch; starchphosphate; sodium alginate and propylene glycol alginate; gelatin;amino-containing acrylic acid copolymers and quaternization productsderived therefrom; and the like.

In certain embodiments, the emulsifying agent is a cellulose ether,particularly a nonionic cellulose ether, such as carboxymethylcellulose.Carboxymethylcellulose is available from a variety of commercialsources, including but limited to, Sigma, Hercules, Fluka and Noviant.In certain embodiments, the average molecular weight of the celluloseether is 1000 daltons or higher, such as 5000 daltons or higher, wherethe average molecular weight may be as high as 10,000 daltons or higher,e.g., 50,000 daltons or higher, 100,000 daltons or higher, and ranges incertain embodiments from 5,000 to 100,000 daltons, such as from 10,000to 50,000 daltons.

The proportion of the emulsifying agent in the cement in certainembodiments ranges from 0.01 to 10% (w/w), such as from 0.05 to 2.0%(w/w).

During use, the cement dry reactant component is combined with a settingfluid. Setting fluids of interest vary, and include a variety ofphysiologically compatible fluids, including, but not limited to: water(including purified forms thereof), aqueous alkanol or polyol solutions,e.g., glycerol, where the alkanol or polyol is present in minor amounts,such as less than 20 volume percent; pH buffered or non-bufferedsolutions; solutions of an alkali metal hydroxide, acetate, phosphate orcarbonate, particularly sodium, more particularly sodium phosphate orcarbonate, e.g., at a concentration in the range of 0.01 to 2M, such asfrom 0.05 to 0.5M, and at a pH in the range of 6 to 11, such as from 7to 9, including from 7 to 7.5; and the like.

Setting fluids of the invention include a cellulose component, such thatthey are cellulosic setting fluids. Of interest are water-solublecellulose components, where specific cellulose components of interestinclude, but are not limited to: nonionic cellulose ethers, such as butnot limited to: methylcellulose, ethylcellulose, hydroxymethylcellulose,hydroxyethylcellulose, carboxymethylcellulose, carboxyethylcellulose andhydroxypropylcellulose; additional celluloses, such ascarboxymethylcellulose sodium, carboxymethylcellulose calcium, etc. Incertain embodiments, the cellulose is carboxymethylcellulose.Carboxymethylcellulose is available from a variety of commercialsources, including but limited to, Sigma, Hercules, Fluka and Noviant.In certain embodiments, the average molecular weight of the cellulose is1000 daltons or higher, such as 5000 daltons or higher, where theaverage molecular weight may be as high as 10,000 daltons or higher,e.g., 50,000 daltons or higher, 100,000 daltons or higher, and ranges incertain embodiments from 5,000 to 100,000 daltons, such as from 10,000to 50,000 daltons.

While the concentration of the cellulose in the setting fluid may vary,in some instances the concentration ranges from 0.5 to 5, such as 1 to 3and including 2 to 3.

In some instances, the setting fluid is not a silicate setting fluid,i.e., the setting fluid does not include a silicate. As such, thesetting fluid is not a silicate setting fluid as described in U.S. Pat.No. 6,375,935.

In certain embodiments, the setting fluid may further include an amountof phosphate ion, as described in U.S. Application Publication No.20040250730; the disclosure of which is herein incorporated by referencein its entirety. For example, the concentration of phosphate ion in thesetting fluid may vary, but may be 0.01 mol/L or greater, such 0.02mol/L or greater and including 0.025 mol/L or greater, where theconcentration may range from 0.01 to 0.5, such as from 0.01 to 0.25,including from 0.02 to 0.2 mol/L. The desired phosphate concentrationmay be provided using any convenient phosphate source, such as anon-calcium-containing salt of phosphoric acid that is sufficientlysoluble, e.g., Na₃PO₄, Na₂HPO₄, or NaH₂PO₄. Salts of other cations suchas K⁺, NH₄ ⁺, etc., may also be employed.

Aspects of the invention include the presence of cyclodextrin in thecomposition prepared from the dry reactants and the setting fluid.Depending on the desired format, the cyclodextrin may be present in thedry reactants or in the setting fluid. By cyclodextrin is meant a cyclicoligosaccharide or mixture of cyclic oligosaccharides, composed of 5 ormore α-D-glucopyranoside units that exhibit a 1→4 linkage. Cyclodextrinsof interest include α-cyclodextrin, β-cyclodextrin and γ-cyclodextrin.The amount of cyclodextrin that is present in either the liquid or drycomponents may vary, depending on the amount that is desired in theflowable composition produced therefrom. In some instances, the amountof cyclodextrin that is desired in the flowable composition producedupon combination of the dry reactants and setting fluid ranges from 0.01to 10% (w/w), such as 0.05 to 2.0% (w/w). In some instances where thecyclodextrin is present in the dry reactant component, the amount ofcyclodextrin that is present in the dry reactant component ranges from0.01 to 10% by weight, such as 0.05 to 2.0% by weight. Cyclodextrincomponents and details regarding the same are further described in U.S.patent application Ser. No. 12/568,531; the disclosure of which isherein incorporated by reference.

In certain embodiments, the cement may further include a contrast orimaging agent, where the contrast agent may be present in one or both ofthe liquid and dry components, or separate therefrom until combinationof all of the components to produce the flowable composition. Contrastagents of interest include, but are not limited to: the water solublecontrast agents described in U.S. Pat. No. 7,306,786, the disclosure ofwhich is herein incorporated by reference in its entirety; and thebarium appetite contrast agents described in U.S. application Ser. No.10/851,766 (Published as US20050257714), the disclosure of which isherein incorporated by reference in its entirety.

One or both of the above liquid and dry reactant components may includean active agent that modulates the properties of the product into whichthe flowable composition prepared by the subject method sets. Suchadditional ingredients or agents include, but are not limited to:organic polymers, e.g., proteins, including bone associated proteinswhich impart a number of properties, such as enhancing resorption,angiogenesis, cell entry and proliferation, mineralization, boneformation, growth of osteoclasts and/or osteoblasts, and the like, wherespecific proteins of interest include, but are not limited to:osteonectin, bone sialoproteins (Bsp), α-2HS-glycoproteins, boneGla-protein (Bgp), matrix Gla-protein, bone phosphoglycoprotein, bonephosphoprotein, bone proteoglycan, protolipids, bone morphogenicprotein, cartilage induction factor, platelet derived growth factor,skeletal growth factor, and the like; particulate extenders; inorganicwater soluble salts, e.g., NaCl, calcium sulfate; sugars, e.g., sucrose,fructose and glucose; pharmaceutically active agents, e.g., antibiotics;and the like. Additional active agents of interest include osteoclastinduction agents, e.g., RANKL, as described in U.S. Pat. No. 7,252,833,the disclosure of which is herein incorporated by reference in itsentirety.

To prepare flowable compositions from the dry reactants and settingfluids, suitable amounts of the dry reactants and the setting fluid arecombined to produce a settable or flowable composition. In other words,the ratio of the dry reactants to setting fluid (i.e. the liquid tosolids ratio) is selected to provide for a “settable” or “flowable”composition, where by “settable” or “flowable” composition is meant acomposition that goes from a first non-solid (and also non-gaseous)state to a second, solid state after setting. In some embodiments, theliquid to solids ratio is chosen to provide for a flowable compositionthat has a viscosity ranging from that of milk to that of modeling clay.As such, the liquids to solids ratio employed in the subject methods mayrange from 0.2 to 1.0, such as from 0.3 to 0.6. Of interest in certainembodiments are methods that produce a paste composition, where theliquid to solids ratio employed in such methods may range from 0.25 to0.5, such as from 0.3 to 0.45.

As mentioned above, the requisite amounts of dry reactants and settingfluid are combined under conditions sufficient to produce the flowableproduct composition. As such, the dry and liquid components may becombined under agitation or mixing conditions, such that a homogenouscomposition is produced from the dry and liquid components. Mixing maybe accomplished using any convenient means, including manual mixing asdescribed in U.S. Pat. No. 6,005,162 and automated mixing as describedin WO 98/28068, the disclosures of which are herein incorporated byreference in their entirety. Also of interest is the device disclosed inU.S. Pat. No. 5,980,482, the disclosure of which is herein incorporatedby reference in its entirety. Of interest in certain embodiments are thestorage/mixing elements disclosed in U.S. Pat. Nos. 6,375,935 and6,719,993; as well as U.S. application Ser. No. 10/462,075 (Published asUS20040250730); U.S. Pat. No. 7,306,786; U.S. Pat. No. 7,252,833; U.S.application Ser. No. 10/851,766 (Published as US20050257714); U.S. Pat.No. 7,261,717; U.S. Pat. No. 7,252,672; and U.S. Pat. No. 7,252,841; thedisclosures of which are herein incorporated by reference in theirentirety.

The temperature of the environment in which combination or mixing of thedry and liquid components takes place is sufficient to provide for aproduct that has desired setting and strength characteristics, and mayrange from 0 to 50° C., such as from 15 to 30° C., including 15 to 25°C., e.g., 16 to 18.5° C. or 22.5 to 25° C. In certain instances, mixingoccurs at a temperature that is: 15° C., 16° C., 17° C., 18° C., 19° C.,20° C., 21° C., 22° C., 23° C., 24° C. and 25° C., or a temperature inbetween any sequential two of these temperatures.

Mixing takes place for a period of time sufficient for a flowablecomposition to be produced, and may take place for a period of timeranging from 15 to 120 seconds, such as from 15 to 100 seconds andincluding from 15 to 60 seconds, e.g., 15 to 50 seconds, 15 to 30seconds, etc.

The above-described protocols result in the production of a flowablecomposition that is capable of setting into a calcium phosphate mineralproduct, as described in greater detail below.

The flowable compositions produced by the above-described methods arecompositions that set into a biologically compatible, and oftenresorbable and/or remodelable, product, where the product ischaracterized by including calcium phosphate molecules not present inthe initial reactants, i.e., that are the product of a chemical reactionamong the initial reactants.

The term flowable is meant to include paste-like compositions, as wellas more liquid compositions. As such, the viscosity time of the subjectflowable compositions, defined as time periods under which the mixedcomposition injects through a standard Luer-lok fitting after mixing,typically ranges up to 10 minutes, usually up to 7 minutes, such as upto 4 minutes. Of interest in certain embodiments are paste compositionsthat have an injectable viscosity that injects in a time period rangingup to 5 minutes, such as up to 4 minutes. Pastes that stay paste-likefor longer period may be displaced by bleeding bone once implanted intothe body, which create a blood interface between the cement and the boneprior to the cement hardening.

The compositions produced by the subject invention set into calciumphosphate mineral containing products. By “calcium phosphate mineralcontaining” product is meant a solid product that includes one or more,usually primarily one, calcium phosphate mineral. In many embodiments,the calcium phosphate mineral is one that is generally poorlycrystalline, so as to be resorbable and, often, remodelable, over timewhen implanted into a physiologically site. The calcium to phosphateratio in the product may vary depending on particular reactants andamounts thereof employed to produce it, but typically range from 2:1 to1.33:1, usually from 1.8:1 to 1.5:1 and more usually from 1:7:1 to1.6:1. Of interest in certain embodiments are apathetic products, whichapathetic products have a calcium to phosphate ratio ranging from 2.0:1to 1.33:1, including both hydroxyapatite and calcium deficient analogsthereof, including carbonate substituted hydroxyapatite (i.e. dahllite),etc. The subject paste-like composition is, in certain embodiments, onethat is capable of setting into a hydroxyapatitic product, such as acarbonated hydroxyapatite, i.e. dahllite, having a carbonatesubstitution of from 2 to 10%, usually from 2 to 8% by weight of thefinal product.

The period of time required for the compositions to harden or “set” mayvary. Set time is determined using the Gilmore Needle Test (ASTMC266-89), modified with the cement submerged under 37° C. physiologicalsaline. The set times of the subject cements may range from 30 secondsto 30 minutes, and will usually range from 2 to 15 minutes and moreusually from 4 to 12 minutes. In certain embodiments, the flowablecomposition sets in a clinically relevant period of time. By clinicallyrelevant period of time is meant that the paste-like composition sets inless than 20 minutes, usually less than 15 minutes and often in lessthan 10 minutes, where the composition remains flowable for 1 minute orlonger, usually 2 minutes or longer and, in many embodiments, for 5minutes or longer following combination or mixture of the precursorliquid and dry cement components.

In some instances, the compositions rapidly set into a high strengthproduct, as determined by the ASTM C403/C403M-06 modified test describedin the experimental section below. In some instances, the compositionsattain high strength rapidly, such that they may be viewed as rapidstrength attainment compositions. As such, at 4 minutes the compositionsof certain embodiments have a setting value of 1000 Newtons or greater,such as 1200 Newtons or greater, where the setting value may be as highas 1300 or 1400 Newtons or greater. At 6 minutes the compositions mayhave a setting value of 1500 Newtons or greater, such as 1700 Newtons orgreater, including 1800 Newtons or greater, e.g., 1900 Newtons orgreater or 2000 Newtons or greater.

The compressive strength of the product into which the flowablecomposition sets may vary significantly depending on the particularcomponents employed to produce it. Of particular interest in manyembodiments is a product that has a compressive strength sufficient forit to serve as at least a cancellous bone structural material. Bycancellous bone structural material is meant a material that can be usedas a cancellous bone substitute material as it is capable ofwithstanding the physiological compressive loads experienced bycompressive bone under at least normal physiological conditions. Assuch, the subject flowable paste-like material is one that sets into aproduct having a compressive strength of 20 or greater, such as 40 andgreater, and including 50 or greater MPa, as measured by the assaydescribed in Morgan, E F et al., 1997, Mechanical Properties ofCarbonated Apatite Bone Mineral Substitute: Strength, Fracture andFatigue Behavior. J. Materials Science: Materials in Medicine. V. 8, pp559-570, where the compressive strength of the final apathetic productmay be as high as 60 MPa or higher. Compressive strengths can beobtained that range as high 100 to 200 MPa.

The resultant product may have a high tensile strength. Tensile strengthis determined using the protocol described in the experimental sectionbelow, and where the products may exhibit a 24-hour tensile strength of5 MPa or greater, such as 7 MPa or greater, e.g., 7.5 to 8 MPa.

In certain embodiments, the resultant product is stable in vivo forextended periods of time, by which is meant that it does not dissolve ordegrade (exclusive of the remodeling activity of osteoclasts) under invivo conditions, e.g., when implanted into a living being, for extendedperiods of time. In these embodiments, the resultant product may bestable for 4 months or longer, 6 months or longer, 1 year or longer,e.g., 2.5 years, 5 years, etc. In certain embodiments, the resultantproduct is stable in vitro when placed in an aqueous environment forextended periods of time, by which is meant that it does not dissolve ordegrade in an aqueous environment, e.g., when immersed in water, forextended periods of time. In these embodiments, the resultant productmay be stable for 4 months or longer, 6 months or longer, 1 year orlonger, e.g., 2.5 years, 5 years, etc.

In certain embodiments of interest, the product that is produced is acomposite product, which includes some unreacted particles, e.g., fromthe coarse particulate reactant, present in the final product. Incertain of the embodiments where such a cement is implanted into an invivo site, the unreacted particles may dissolve (e.g., via resorption)over time leaving a porous structure at the implant site, where theporous structure remains until it is remodeled. In certain embodiments,the remaining coarse particles in the composite may have a differentradiopacity than the remainder of the product, e.g., where at least aportion of the coarse particles in the cement were dolomite.

In certain embodiments, the flowable paste-like composition is capableof setting in a fluid environment, such as an in vivo environment at abone repair site. As such, the flowable paste composition can set in awet environment, e.g., one that is filled with blood and otherphysiological fluids. Therefore, the site to which the flowablecomposition is administered during use need not be maintained in a drystate.

In certain embodiments, the subject cement compositions may be seededwith any of a variety of cells, as described in published U.S. PatentPublication No. 20020098245, the disclosure of which is hereinincorporated by reference in its entirety.

In addition, in certain embodiments the compositions includedemineralized bone matrix, which may be obtained typically in alyophilized or gel form and is combined with the cement composition atsome prior to implantation. A variety of demineralized bone matrixes areknown to those of skill in the art and any convenient/suitable matrixcomposition may be employed.

In certain embodiments, the cements may include one or more collectionsof contrast particles (for example, for use as tracers during use of thecement), e.g., as described in U.S. Pat. No. 6,273,916 or U.S.application Ser. Nos. 10/62,931 and 10/851,766; the disclosures of whichare herein incorporated by reference in their entirety.

Applications

Flowable compositions produced from cements of the invention, e.g., asdescribed above, find use in applications where it is desired tointroduce a flowable material capable of setting up into a solid calciumphosphate product into a physiological site of interest, such as indental, craniomaxillofacial and orthopedic applications. In orthopedicapplications, the cement may be prepared, as described herein, andintroduced or applied to a bone repair site, such as a bone sitecomprising cancellous and/or cortical bone. In some instances, the siteof application is a cancellous bone void that results from reducing afracture. In these instances, the methods may include reducing a bonefracture and then applying an amount of the flowable composition to theresultant void, where the amount may be sufficient to substantially ifnot completely fill the void.

Orthopedic applications in which the cements prepared by the subjectsystem find use include, but are not limited to, the treatment offractures and/or implant augmentation, in mammalian hosts, particularlyhumans. In such fracture treatment methodologies, the fracture is firstreduced. Following fracture reduction, a flowable structural materialprepared by the subject system is introduced into the cancellous tissuein the fracture region using the delivery device described above.Specific dental, craniomaxillofacial and orthopedic indications in whichthe subject invention finds use include, but are not limited to, thosedescribed in U.S. Pat. No. 6,149,655, the disclosure of which is hereinincorporated by reference in its entirety. In addition to theseparticular applications described in this U.S. Patent, the subjectcement compositions also find use in applications where a sternotomy hasbeen performed. Specifically, the subject cements find use in theclosure process of a sternotomy, where the bone fragments are rejoinedand wired together, and any remaining cracks are filled with the subjectcement. In yet other embodiments, the subject compositions find use indrug delivery, where they are capable of acting as long lasting drugdepots following administration to a physiological site. See e.g. U.S.Pat. Nos. 5,904,718 and 5,968,253; the disclosures of which are hereinincorporated by reference in their entirety.

Representative applications of interest also include, but are notlimited to: those described in U.S. Pat. Nos. 6,375,935 and 6,719,993;as well as U.S. application Ser. No. 10/462,075 (Published asUS20040250730); U.S. Pat. No. 7,306,786; U.S. Pat. No. 7,252,833; U.S.application Ser. No. 10/851,766 (Published as US20050257714); U.S. Pat.No. 7,261,717; U.S. Pat. No. 7,252,672; and U.S. Pat. No. 7,252,841; thedisclosures of which are herein incorporated by reference in theirentirety.

Kits

Also provided are kits that include the subject cements, where the kitsat least include a dry particulate component and a cellulose containingsetting fluid, as described above. When both a dry component and settingfluid are present, the dry component and setting fluid may be present inseparate containers in the kit, or some of the components may becombined into one container, such as a kit wherein the dry componentsare present in a first container and the liquid components are presentin a second container, where the containers may or may not be present ina combined configuration, as described in U.S. Pat. No. 6,149,655, thedisclosure of which is herein incorporated by reference in its entirety.In addition to the cement compositions, the subject kits may furtherinclude a number of additional reagents, e.g., cells (as describedabove, where the composition is to be seeded), protein reagents (asdescribed above), and the like.

In certain embodiments, the subject cements may be kilted as describedin U.S. Pat. No. 6,273,916, the disclosure of which is hereinincorporated by reference in its entirety, e.g., packaged in a kit withat least two different sterilized pouches (or analogous compartments) ofcement that may independently used at the same or different times, whereeach pouch may include the same or different cement formulation, e.g.,where the cements may differ in terms of contrast characteristics.

In certain embodiments, the kits may further include mixing and/ordelivery elements, e.g., mortar and pestle, spatula, etc., whichelements find use in, e.g., the preparation and/or delivery of thecement composition.

In addition to above-mentioned components, the subject kits typicallyfurther include instructions for using the components of the kit topractice the subject methods. The instructional material may also beinstructional material for using the cement compositions, e.g., it mayprovide surgical techniques and principals for a particular applicationin which the cement is to be employed. The instructions for practicingthe subject methods are generally recorded on a suitable recordingmedium. For example, the instructions may be printed on a substrate,such as paper or plastic, etc. As such, the instructions may be presentin the kits as a package insert, in the labeling of the container of thekit or components thereof (i.e., associated with the packaging orsubpackaging) etc. In other embodiments, the instructions are present asan electronic storage data file present on a suitable computer readablestorage medium, e.g. CD-ROM, diskette, etc. In yet other embodiments,the actual instructions are not present in the kit, but means forobtaining the instructions from a remote source, e.g. via the internet,are provided. An example of this embodiment is a kit that includes a webaddress where the instructions can be viewed and/or from which theinstructions can be downloaded. As with the instructions, this means forobtaining the instructions is recorded on a suitable substrate.

Systems

Also provided are systems that find use in practicing the subjectmethods, as described above. The subject systems at least include dryand liquid components of a cement, as described above, and a mixingelement. In certain embodiments, the systems may further includeadditional agents, e.g., contrast agents, active agents, etc., asdescribed above.

The following examples are offered by way of illustration and not by wayof limitation.

EXPERIMENTAL

The effective working temperature at which calcium phosphate cements canbe utilized ranges from 19° C. to 22° C. Calcium phosphate cements aretemperature sensitive when utilized outside the above-specified range.Below 19° C., calcium phosphate cements tend to be very runny and showsigns of decreased mechanical properties. Above 22° C., many calciumphosphate cements tend to be dry and crumble after mixing, presentingproblems during use, e.g., injection into a bone repair site. Suchproblems limit the use of calcium phosphate cements in the surgicalfield.

In the following experimental section, an extension in the workingtemperature range of a calcium phosphate cement is reported. The workingtemperature range is extended from 16° C. to 25° C. while maintainingthe calcium phosphate cements' mechanical properties. This increase inworking temperature range is attributed to the use of 2.5 wt. %carboxymethyl cellulose (CMC) solution. For impactable formulations,usage of 2.5 wt. % carboxymethyl cellulose solution is sufficient toincrease the working temperature range. For injectable formulations,carboxymethyl cellulose (CMC) is utilized both in solution as well aspowder component of the cement. The cements' mechanical properties areexamined and compared with the control (that is, the currentformulation). For impactable formulations, the results show that the mixconsistency is great at both the temperatures, that is, it is not runnyat low temperatures and it is not dry at high temperatures. Forinjectable formulations, the results show a consistent injection load atboth 16° C. and 25° C., while displaying similar mechanical properties.

I. Test Formulations

Material Range Average A. FORMULATION #1 - Impactable form (5 cc kitsize) SPMA = 0.099-0.119 grams 0.109 grams 106-212 μm α-TCP* =3.070-3.110 grams 3.090 grams 2 μm α-TCP = 6.470-6.490 grams 6.480 gramsTotal average powder weight = 9.679 grams Liquid (2.5 wt. % CMC soln.) =2.990-3.010 grams  3.00 grams Liquid to powder ratio = 0.31 B.FORMULATION #2 - Injectable form (5 cc kit size) CMC = 0.019-0.021 grams0.020 grams SPMA = 0.068-0.078 grams 0.073 grams 38-106 μm α-TCP* =1.506-1.526 grams 1.516 grams 106-212 μm α-TCP* = 1.506-1.526 grams1.516 grams 2 μm α-TCP = 6.060-6.080 grams 6.070 grams Total averagepowder weight = 9.195 grams Liquid (2.5 wt. % CMC soln.) =  3.30-3.320grams  3.31 grams Liquid to powder ratio = 0.36 *particles synthesizedby process C as described in U.S. application Ser. No. 12/328,720 and asthe process described in U.S. application Ser. No. 12/568,531; thedisclosures of which are herein incorporated by reference.II. Control Formulations

Material Range Average A. CONTROL FORMULATION #1 - Impactable form (5 cckit size) CMC = 0.018-0.028 grams 0.023 grams SPMA = 0.099-0.119 grams0.109 grams 106-212 μm α-TCP⁺ = 3.070-3.110 grams 3.090 grams 2 μm α-TCP= 6.470-6.490 grams 6.480 grams Total average powder weight = 9.702grams Liquid (dil. Na-silicate soln.) = 3.715-3.755 grams 3.735 gramsLiquid to powder ratio = 0.38 B. CONTROL FORMULATION #2 CMC =0.023-0.033 grams 0.028 grams SPMA = 0.063-0.083 grams 0.073 grams38-106 μm α-TCP⁺ = 1.812-1.832 grams 1.822 grams 106-212 μm α-TCP⁺ =1.205-1.225 grams 1.215 grams 2 μm α-TCP = 6.060-6.080 grams 6.070 gramsTotal average powder weight = 9.208 grams Liquid (dil. Na-silicatesoln.) = 3.847-3.887 grams 3.867 grams Liquid to powder ratio = 0.42⁺particles synthesized as described in PCT application Ser. No.PCT/US2005/026369 and published as WO/2006/014886III. Mixing Protocol

For both formulations, the powder and liquid are mixed using a mortarand pestle to produce paste which is then allowed to set and tested asdescribed above

IV. Setting Strength

A. Methods

A modification of the standard setting test described in ASTMC4031C403M-06 is employed, in which the load required to drive needles aprescribed distance into concrete or a similar setting material ismeasured. The modification involves a needle with a tip configurationsimilar to that used in ASTM C266-07. A modified high load indentor (7mm in diameter) is attached to Instron material testing machine with amaximum load of 5000 N. The needle is pushed 1.25 mm at a rate of 15.2mm/s into the sample cured at 32±0.5° C. and 100% RH. No spring loadaverage is calculated or used in later calculations (the high loadindentor test fixture does not use a spring).

B. Results

An indentation load in excess of 3.5 MPa (135 Newton) has beendetermined as the time of initial setting according to the standard ofASTM C403/C403M-06.

Control Test Form #1  4 min Setting Strength 600N 1600N (Impact)  6 minSetting Strength 1000N  1850N Form #2  6 min Setting Strength 500N  800N(Inject) 10 min Setting Strength 900N 1200N

As can be seen from the above results, inclusion of 2.5 wt. % CMCsolution significantly increases the setting strength as compared to thecontrol

V. Injection test

A. Methods

This test is a modification of the extrusion test performed in ASTMF451-86 for polymethylmethacrylate (PMMA) bone cements on a capillaryrheometer. The test is performed at 3 minutes post-mix by allowing thecompression platen to make contact with the syringe plunger in adownward direction at 5.1 cm/minute. The test is terminated at a load of75 N and the remaining volume is noted.

B. Results

This test was performed for formulation #2 since it is the injectableform. Full injection, that is, 0 cc leftover in the syringe isdetermined as a criteria for injection test.

Test Temperature Control Test Form #2 16° C. Runny -does not Fullinjection behave as inject (0 cc leftover) (Inject) 25° C. 2.0 ccleftover Full injection (0 cc leftover)As can be seen from the above results, inclusion of 2.5 wt. % CMCsolution significantly increases the injection ability of the cements atsevere temperatures in comparison to the control.VI. Tensile StrengthA. Methods

The testing was conducted using an Instron mechanical testing system(Canton, Mass.). The test specimens were circular rings of 0.5″ I.D. and0.3″ thickness that were filled with the cement using a spatula. Thefilled molds were placed into a phosphate buffered saline bathmaintained at 37° C. and allowed to cure for 24 hours. Samples were thenremoved from the unit, placed on a steel platen and crushed at a crosshead speed of 0.1 inches/minute. Ultimate tensile stress was calculatedusing the following equation:Equation of tensile stress: σ=2 P/πD t

where:

-   -   P=ultimate compressive load, Newtons    -   D=sample diameter, millimeters    -   t=sample thickness, millimeters.        B. Results

Control Test Form #1 24 hr Tensile Strength 4.5 MPa 5.2 MPa Form #2 24hr Tensile Strength 4.3 MPa 4.7 MPa

As can be seen from the above results, inclusion of 2.5 wt. % CMCsolution maintains the tensile strength as compared to the control.

VII. Compressive Strength

A. Methods

The compressive strength test is a modification of ASTM F 451. Theprimary difference from the ASTM method is that pressurization of thevoid filler specimens is not required. Additional modifications to thetest involve curing the bone void filler specimens for 24 hours in a 37°C. phosphate buffered saline environment at pH=7.4 and sanding the endsof the specimens before removing them from the mold for testing. Eachspecimen is placed between the loading platens of the mechanical testingsystem. Specimens are loaded along the longitudinal axis at displacementrate of 0.1 in./min until failure. Load, displacement, and time arerecorded continuously at a sampling rate of 10 Hz.

B. Results

The compressive strength for both test formulation 1 and 2 above wasfound to be 55 MPa.

All publications and patent applications mentioned in this specificationare herein incorporated by reference to the same extent as if eachindividual publication or patent application was specifically andindividually indicated to be incorporated by reference.

The invention now being fully described, it will be apparent to one ofskill in the art that many changes and modifications can be made theretowithout departing from the spirit and scope of the appended claims.

What is claimed is:
 1. A method of producing a flowable composition thatsets into a calcium phosphate containing product, the method comprising:combining: (a) a dry reactant component comprising: (i) a firstparticulate calcium phosphate reactant having a mean particle size of 8μm or less; and (ii) a second particulate calcium phosphate reactanthaving a mean particle size of 10 μm or greater; and (b) a liquidcomponent consisting of water as setting fluid andcarboxymethylcellulose in amount ranging from about 2 up to about 3 wt%, wherein the dry reactant component and the setting fluid are combinedin a ratio sufficient to produce the flowable composition that sets intoa calcium phosphate containing product.
 2. The method according to claim1, wherein the first and second particulate calcium phosphate reactantsare present in the dry reactant component in a ratio that ranges from 1to
 10. 3. The method according to claim 2, wherein the first and secondparticulate calcium phosphate reactants are tricalcium phosphate.
 4. Themethod according to claim 1, wherein the first particulate calciumphosphate reactant has a mean particle size of 4 μm.
 5. The methodaccording to claim 1, wherein the dry reactant component and settingfluid are combined at a temperature ranging from 15 to 25° C.
 6. Themethod according to claim 1, wherein the dry reactant component and thesetting fluid are combined at a temperature ranging from 16 to 18.5° C.7. The method according to claim 1, wherein the dry reactant componentand the setting fluid are combined at a temperature ranging from 22.5 to25° C.
 8. The method according to claim 1, wherein the secondparticulate calcium phosphate reactant comprises a tricalcium phosphatecoarse particulate composition comprising tricalcium phosphate particlesthat range in size from 30 to 250 μm and comprise sodium in an amountranging from 1500 to 2500 ppm.
 9. The method according to claim 1,wherein the dry reactant component comprises a dry cellulose.
 10. Themethod according to claim 9, wherein the dry cellulose iscarboxymethylcellulose.
 11. The method according to claim 1, wherein theconcentration of the amount of carboxymethylcellulose in the settingfluid is 2.5 wt. %.
 12. The method according to claim 1, wherein thefirst and second particulate calcium phosphate reactants areα-tricalcium phosphate.
 13. The method according to claim 1, wherein theratio in weight of setting fluid to dry reactants is in the range from0.3 to 0.6.
 14. The method according to claim 1, wherein the first andsecond particulate calcium phosphate reactants are tricalcium phosphate,and wherein the second particulate calcium phosphate reactant comprisesa tricalcium phosphate coarse particulate composition comprisingtricalcium phosphate particles that range in size from 30 to 250 μm andcomprise sodium in an amount ranging from 1500 to 2500 ppm.